In their new study, the Oxford scientists tested seven captive New Caledonian crows on a range of tasks requiring the use of up to three different tools in a sequence to retrieve food. Five crows successfully used tools in a sequence (four from their very first trial), and four repeatedly solved the most demanding three-tool condition. In this, food was placed at a depth so that it was only reachable with one particular tool, but getting that tool required the use of two other others. The crows had to use a short, available tool to drag in a longer, otherwise out-of-reach tool, and then use that longer tool to retrieve the correct, longest one. They could then use the longest tool to reach for the food morsel.
Pre-training on each element in the sequence was not required for successful sequential tool use - an explanation that could not be ruled out in earlier studies on primates and crows. Painstaking analysis of tool choices, tool swapping and improvement over time allowed the team to conclude that successful crows did not probe for tools at random: for example, when birds swapped tools, it was usually to get a longer one. At the same time, however, they could find no firm evidence to support previous claims that sequential
tool use demonstrates analogical reasoning or human-like planning.
While the ability of crows to use three tools in sequence reveals a competence beyond that observed in any other non-human species, including non-human primates, this study also emphasises the importance of a cautious approach in comparative cognitive science. Seemingly intelligent behaviour can be achieved without the involvement of high-level mental faculties, and detailed analyses are necessary before accepting claims for complex cognitive abilities.
